In World War II, the United States mobilized an Army of 91 divisions, two of which were inactivated.1 The remaining 89 divisions were employed overseas, and after entering the theaters all were maintained at or near their table of organization strength. In this respect the experience of World War I had been very different. At the time of the armistice in November 1918, 58 divisions had been activated, but only 42 had been shipped overseas. Twelve of these 42 divisions were not functioning as combat units, having been drained for replacements or converted to other uses in France. Of the 16 divisions forming at home, 9 were at less than half strength in November 1918, and one recently activated division could boast of only a single enlisted man.2 This situation in 1918 reflected the fact that the war ended before mobilization in the United States was complete. But it reflected also the fact that the War Department was unable to maintain at full strength the Army that it had projected, and that some divisions had to be dissolved, or never filled, in order that others might have enough manpower to enter or remain in combat.

It was therefore a considerable achievement, by the standards of World War I, not only to raise 91 divisions in World War II, but also to maintain 89 at effective strength as combat units, replacing losses without dissolution of any divisions committed to action, although some divisions suffered heavy and continuous losses over a period of years. By 31 January 1945, 47 infantry regiments in 19 Infantry divisions had lost from 100 percent to over 200 percent of their strength in battle casualties alone.3 By May 1945 the 5 hardest hit divisions had suffered 176 percent battle casualties in all components.4 Yet substantially all losses were replaced.5

Seen in another light, a ground army of 89 divisions was a modest creation. The Germans mobilized over 300 divisions, the Japanese about 100. Though not all enemy divisions were kept as nearly at effective strength as were the American, the preponderance was still heavily on the enemy side. British ground forces did not suffice to redress the balance. Success of American ground forces therefore depended heavily on a number of other factors. One was the Russian Army, which was estimated to have over 400 divisions in 1945, and which engaged the mass of the German combat power, as well as neutralizing certain Japanese forces on the Manchurian border. Another was Allied naval strength, which enabled American ground forces to attack at advantageous times and places. A third was Allied air power, which enabled ground forces to attack an enemy underequipped, disrupted, and immobilized by bombing. To the strengthening of these other factors the United States devoted the bulk of its resources and its manpower. At the beginning of 1945 the United States had spent over ten times as much, in terms of dollars, on World War II as on World War I. The total armed forces of the United States were well over twice as large as in November 1918. But the size of combatant ground forces was not much greater than in 1918. Because the divisions of the later war were much smaller than those of the earlier, the 89 divisions of 1945 included only 25 percent more manpower than the divisions of 1918. (see Table I.)

The ground forces of World War II proved to be none too large. In 1918 American troops were needed only in France. After 1941 they were needed on opposite sides of the globe. (See Table II.) More United States ground forces were required in Europe in 1914 than had been expected. Despite the tremendous victories of the Russians, and despite control of the sea and air by the western Allies, all American ground forces were committed when Germany surrendered in May 1945. At that time over 96 percent of tactical troops of the Army Ground Forces were overseas, and the last divisions had been dispatched three months before. No more combat units were forming at home. No reserve, other than replacements, remained in the United States. Nor was there any

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significant strategic reserve of uncommitted forces in the theaters. This may be interpreted either as remarkably accurate planning of the minimum forces required or as a fairly narrow escape from disagreeable eventualtiesówinning by the skin of the teeth.

With so relatively few divisions, every division in the theater had to be used to the utmost. This disadvantage was aggravated by the fact that, with many other demands for space, divisions were shipped to the theaters rather slowly. It was difficult, and in some theaters impossible, to withdraw divisions from combat for periods of rest. During periods of intensive combat an infantry division suffered about 100 percent losses in its infantry regiments every three months. While the gaps caused by these losses were generally filled by the continuous stream of replacements, divisions suffered in efficiency with such a high turnover of infantry. A severe mental strain was imposed on the individual soldier, especially the infantryman, who felt that no matter how long he fought or how long he survived the dangers of combat he must remain in action until removed as a casualty. Cases of battle neurosis multiplied from this cause. Or men simply became tired, and when tired more easily got themselves killed, wounded, or captured. The stream of replacements thus flowed into somewhat leaky vessels. Had more units been available to relieve units in battle, not only would the strain of combat soldiers have been eased, but some saving of manpower would probably have resulted.

The present study traces the process, so far as it was known at the headquarters
of the Army Ground Forces, by which the United States combatant ground army
of World War II was planned, mobilized, and maintained at effective strength.
Other studies in the present series are closely related. Study
No. 3 presents a view of mobilization in tabular form. Study No. 7 deals
with the replacement system, by which units once mobilized were kept in being.
Problems in the procurement of suitable personnel, and in the training of officers
and specialists for the expanding Army, are treated in Studies Nos. 5, 6, 30,
and 31. In Studies Nos. 12 and 14, which describe the training of infantry divisions
and other units, the reader will find details of the effects on training of
certain difficulties inherent in mobilization, such as the need of supplying
cadres, the shortage of manpower and equipment, the turnover of personnel within
units and consequent need for repeated retraining, and the tapping of units
for replacementsófor the replacement system did not work smoothly to produce
the results noted above. The internal organization of units, and hence the allotment
of manpower and equipment to each unit set up for mobilization, is treated in
Study No. 8. Aspects of the mobilization of armored forces, airborne units,
and heavy artillery are presented in Study No. 9. Attempts to provide combined
training of ground forces with aviation, on which it was foreseen that ground
forces would depend for success, are traced in detail in Study No. 35.